Re: [PATCH bpf-next v4 2/5] libbpf: Store map pin path and status in struct bpf_map

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, Oct 31, 2019 at 10:26 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:
>
> > On Tue, Oct 29, 2019 at 12:39 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
> >>
> >> From: Toke Høiland-Jørgensen <toke@redhat.com>
> >>
> >> Support storing and setting a pin path in struct bpf_map, which can be used
> >> for automatic pinning. Also store the pin status so we can avoid attempts
> >> to re-pin a map that has already been pinned (or reused from a previous
> >> pinning).
> >>
> >> The behaviour of bpf_object__{un,}pin_maps() is changed so that if it is
> >> called with a NULL path argument (which was previously illegal), it will
> >> (un)pin only those maps that have a pin_path set.
> >>
> >> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> >> ---
> >
> > Looks good, thanks! Just some minor things to fix up below.
> >
> > Acked-by: Andrii Nakryiko <andriin@fb.com>
> >
> >>  tools/lib/bpf/libbpf.c   |  164 +++++++++++++++++++++++++++++++++++-----------
> >>  tools/lib/bpf/libbpf.h   |    8 ++
> >>  tools/lib/bpf/libbpf.map |    3 +
> >>  3 files changed, 134 insertions(+), 41 deletions(-)
> >>
> >> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> >> index ce5ef3ddd263..fd11f6aeb32c 100644
> >> --- a/tools/lib/bpf/libbpf.c
> >> +++ b/tools/lib/bpf/libbpf.c
> >> @@ -226,6 +226,8 @@ struct bpf_map {
> >>         void *priv;
> >>         bpf_map_clear_priv_t clear_priv;
> >>         enum libbpf_map_type libbpf_type;
> >> +       char *pin_path;
> >> +       bool pinned;
> >>  };
> >>
> >>  struct bpf_secdata {
> >> @@ -4025,47 +4027,119 @@ int bpf_map__pin(struct bpf_map *map, const char *path)
> >>         char *cp, errmsg[STRERR_BUFSIZE];
> >>         int err;
> >>
> >> -       err = check_path(path);
> >> -       if (err)
> >> -               return err;
> >> -
> >>         if (map == NULL) {
> >>                 pr_warn("invalid map pointer\n");
> >>                 return -EINVAL;
> >>         }
> >>
> >> -       if (bpf_obj_pin(map->fd, path)) {
> >> -               cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
> >> -               pr_warn("failed to pin map: %s\n", cp);
> >> -               return -errno;
> >> +       if (map->pin_path) {
> >> +               if (path && strcmp(path, map->pin_path)) {
> >> +                       pr_warn("map '%s' already has pin path '%s' different from '%s'\n",
> >> +                               bpf_map__name(map), map->pin_path, path);
> >> +                       return -EINVAL;
> >> +               } else if (map->pinned) {
> >> +                       pr_debug("map '%s' already pinned at '%s'; not re-pinning\n",
> >> +                                bpf_map__name(map), map->pin_path);
> >> +                       return 0;
> >> +               }
> >
> > `if (map->pinned)` check is the same in both branches, so I'd do it
> > first, before this map->pin_path if/else.
>
> But it's not. It's debug & return if pin_path is set, and an error
> otherwise.

Ah, right, it did feel weird to duplicate like that :) Ok, never mind then.

>
> Will fix the rest of your nits :)
>
> -Toke